WO2025079466A1 - Pneumatic tire - Google Patents

Abstract

According to the present invention, in the tire radial direction region from a position that is a distance of 2.0 × Hf away from a base line of the applicable rim outward in the tire radial direction to a position that is a distance of 3.0 × Hf away from the base line, the maximum value of the curvature of the carcass folded-back portion is 0.003 (1/mm) or less.

Description

Pneumatic tires

The present invention relates to pneumatic tires, particularly to heavy-duty tires. The present invention relates to large tires (OR (Off-the-Road) tires) such as tires for construction vehicles.

Large tires, such as tires for construction vehicles, generally have a tire structure that has a carcass body made of a carcass ply with rubber-coated carcass cords that span a toroidal shape between a pair of bead cores, and a carcass folded-back portion made of the carcass ply that wraps around each bead core from the carcass body from the inside to the outside of the tire and extends radially outward from the tire.

This type of tire is often used while carrying a heavy load and traveling over rough terrain with bumps and rocks, so it is known to improve the durability of the bead section so that it can withstand use in harsh environments.

However, when a large load is applied and the tire flexes, compressive strain occurs in the carcass folded portion, which contributes to improving the durability of the bead portion. If this compressive strain occurs repeatedly in the carcass folded portion, particularly in harsh environments, fatigue fracture will occur.

Since such fatigue fractures in the carcass folded parts significantly reduce the lifespan of the tire, suppressing fatigue fractures in the carcass folded parts is one of the challenges required for this type of tire.

The occurrence of buckling of the carcass cords, which leads to fatigue fracture of the carcass folded-back portion, is believed to be caused in part by compression strain caused by the carcass folded-back portion being on the compression side in bending deformation that occurs when the bead portion collapses, with the carcass body acting as the neutral axis of bending. Therefore, in order to suppress compression strain in the carcass folded-back portion, it is generally known that a typical method for reducing compression strain is to move the carcass folded-back portion as close as possible to the carcass body.

Furthermore, this method also has the effect of suppressing shear strain of the rubber between the outer surface of the bead portion and the carcass folded portion, which occurs due to deformation of the carcass folded portion at the contact area between the rim flange of the applicable rim and the bead portion, and is also effective in suppressing rubber separation that occurs along the carcass folded portion.

However, simply bringing the carcass folded portion closer to the carcass main body will promote shear distortion of the rubber between the carcass folded portion and the carcass main body, causing separation of the rubber between the carcass folded portion and the carcass main body early in the life of the tire.

Furthermore, even if the carcass fold-up portion and the carcass main body are brought closer together to suppress compression strain, the bending rigidity of the carcass fold-up portion on the outer side of the part where compression strain is suppressed in the tire radial direction will actually be reduced by bringing the carcass fold-up portion closer to the carcass main body.

In other words, moving the carcass folded part closer to the carcass main body is known to be an effective measure for suppressing compression strain in the carcass folded part, but on the other hand, this increases shear strain in the rubber between the carcass folded part and the carcass main body, which reduces the bending rigidity of the carcass folded part, which is a problem.

Therefore, a technology has been proposed in which the carcass shape is configured so that the distance between the cords between the carcass main body and the carcass folded back part gradually decreases from the bead core toward the outside in the tire radial direction, becomes a minimum value, then gradually increases to a maximum value, and then gradually decreases again to a minimum value at the end of the carcass folded back part. When this tire is mounted on an applicable rim, the height from the rim baseline of the applicable rim to the carcass main body points of the minimum and maximum values and the height of the rim flange are adjusted to suppress shear strain of the rubber between the carcass folded back part and the carcass folded back part, and to suppress a decrease in the bending rigidity of the carcass folded back part, thereby reducing the compression strain of the carcass folded back part.

Furthermore, Patent Document 1 proposes a method for further reducing the compression strain occurring in the carcass folded back portion by restricting the ratio b/a of the minimum value a of the distance between the cords of the carcass main body and the carcass folded back portion to a predetermined range.

JP 2009-113715 A

However, the above methods may not always be able to sufficiently reduce fatigue breakage due to buckling in the carcass folded-back portion, and there is room for improvement in the durability of the bead portion.

The present invention aims to provide a pneumatic tire that suppresses buckling of the carcass folded-up portion, thereby suppressing fatigue fracture of the carcass folded-up portion and improving durability of the bead portion.

The gist and configuration of the present invention are as follows.
(1) A pneumatic tire having a carcass skeleton including a carcass body portion formed of a carcass ply having a rubber-coated multiple carcass cords that are toroidally straddled between a pair of bead cores, and a carcass folded-up portion formed of the carcass ply that wraps around each bead core from the carcass body portion from the inside to the outside of the tire and extends radially outward in the tire direction,
In a cross-sectional view in the tire width direction when the pneumatic tire is mounted on the applicable rim,
the inter-cord distance between the carcass main body portion and the carcass folded-back portion gradually decreases from the bead core toward the outside in the tire radial direction, becomes a minimum value once, and then gradually increases to a maximum value,
heights H _A and H _B in the tire radial direction measured from the baseline of the applicable rim to the points of the carcass main body which are the minimum and maximum values, and a flange height H _f of the applicable rim,
1.26× _Hf ≦ _HA ≦2.14× _Hf , and
2.43×H _f ≦H _B ≦3.75×H _f ,
Fulfilling
a ratio b/a of the maximum inter-cord distance b to the minimum inter-cord distance a is greater than 1.00,
a maximum value of a curvature of the carcass folded-up portion in a tire radial direction region from a position spaced a distance of 2.0× _Hf to a position spaced a distance of 3.0× _Hf radially outward from the baseline is 0.003 (1/mm) or less.
Here, "curvature" refers to the curvature at a target position, which is the curvature of a circle passing through a total of three points, that is, the target position point and two points adjacent to each side of the target position point, obtained by obtaining the coordinates of the carcass fold-back portion every 20 mm along the periphery in a cross-sectional view in the tire width direction when the pneumatic tire is mounted on the applicable rim.
Furthermore, the term "applicable rim" refers to a standard rim for an applicable size that is an industrial standard effective in the region where the tire is produced and used, and is described in the JATMA YEAR BOOK of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, the STANDARDS MANUAL of the European Tire and Rim Technical Organization (ETRTO) in Europe, or the YEAR BOOK of the Tire and Rim Association, Inc. (TRA) in the United States, or that will be described in the future (Measuring Rim in the ETRTO STANDARDS MANUAL, and Design Rim in the TRA YEAR BOOK). For sizes not listed in the above industry standards, it refers to a rim with a width that corresponds to the bead width of the tire. "Applicable rim" includes current sizes as well as sizes that may be included in the above industry standards in the future. Examples of "sizes to be listed in the future" include sizes listed as "FUTURE DEVELOPMENTS" in the 2013 edition of the ETRTO STANDARDS MANUAL.

(2) A pneumatic tire having a carcass skeleton including a carcass body portion formed of a carcass ply having a rubber-coated multiple carcass cords that are toroidally straddled between a pair of bead cores, and a carcass folded-up portion formed of the carcass ply that wraps around each bead core from the carcass body portion from the inside to the outside of the tire and extends radially outward from the tire,
In a cross-sectional view in the tire width direction when the pneumatic tire is mounted on the applicable rim,
When the flange height of the applicable rim is _Hf ,
a cord distance between the carcass main body portion and the carcass folded-up portion in a tire radial direction region from a position spaced apart by a distance of 2.0× _Hf to a position spaced apart by a distance of 3.0× _Hf outward in the tire radial direction from a bead baseline of the applicable rim is 0.25 times or more of a maximum diameter of the bead core in a cross section in the tire width direction,
A pneumatic tire, wherein a maximum value of a curvature of the carcass folded-up portion in the tire radial direction region is 0.003 (1/mm) or less.

The present invention provides a pneumatic tire that suppresses buckling of the carcass folded portion, thereby suppressing fatigue fracture of the carcass folded portion and improving durability of the bead portion.

1 is a cross-sectional view in the tire width direction of a pneumatic tire according to one embodiment of the present invention. FIG. 1 illustrates regions where compressive and tensile forces occur. FIG. 1 shows the displacement of compressive and tensile strains. FIG. 1 shows the change in displacement of compressive and tensile strains. 1 is a view showing a widthwise cross section of a portion of a bead portion and a sidewall portion of a pneumatic tire according to one embodiment of the present invention. FIG. 4 is a diagram showing a curvature distribution in the tire radial direction of a carcass folded-up portion. FIG. 4 is a diagram showing a compressive strain distribution in the tire radial direction of a carcass folded-up portion.

Below, an embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 is a cross-sectional view in the tire width direction of a pneumatic tire according to one embodiment of the present invention. Figure 1 is a cross-sectional view in the tire width direction of a pneumatic tire 8 (hereinafter also simply referred to as a tire) mounted on an applicable rim. Figure 1 shows only one half in the tire width direction bounded by the tire equatorial plane, but the other half has a similar configuration. The pneumatic tire 8 is preferably a heavy-duty tire, and in this example is a large tire (OR (Off The Road) tire) such as a tire for construction vehicles.

As shown in FIG. 1, the tire 8 has a bead core 1 embedded in each of a pair of bead portions. The tire 8 has a carcass skeleton made of one or more carcass plies, which are made of a carcass main body portion 2 made of a rubber-coated carcass ply of multiple carcass cords that span a toroidal shape between the pair of bead cores 1, and carcass fold-back portions 3 that wrap around each bead core 1 from the inside to the outside of the tire and extend radially outward from the carcass main body portion 2. The carcass cords can be, for example, steel cords.

A belt 6 is disposed on the radially outer side of the carcass body 2, and a tread portion 7 is provided on the radially outer side of the belt 6. In FIG. 1, the tire 8 is mounted on an applicable rim 4, and FIG. 1 shows the rim flange 5 and the baseline L of the applicable rim 4 (hereinafter referred to as the rim baseline), which passes through the tire equatorial plane and extends parallel to the axis of rotation of the tire 8.

As shown in FIG. 1, the distance between the cords between the carcass main body 2 and the carcass folded-back portion 3 gradually decreases from the vicinity of the bead core 1 toward the outside in the tire radial direction, reaching a minimum value, and then gradually increases toward the outside in the tire radial direction to reach a maximum value.

When a load is applied to the tire, the tire bends, and bending deformation occurs in the bead and part of the sidewall, with the carcass body 2 acting as the neutral axis of bending. As shown in FIG. 2A, bending deformation occurs in the direction of arrow C1 in region C on the radial outside of the rim flange 5, resulting in compressive deformation as shown by arrow C2. Furthermore, bending deformation occurs in region T on the radial outside of region C in the tire, resulting in tensile deformation as shown by arrow T2.

In this way, when the tire is bent, compressive and tensile deformations occur in parts of the bead and sidewall sections, and the compressive and tensile forces associated with these deformations act on the carcass fold-back section 3 in each of these areas. As a result, compressive and tensile strains occur in each of these areas, as shown in Figure 2B.

In response to this, by gradually reducing the distance between the cords between the carcass main body 2 and the carcass folded-back portion 3 to a minimum value, the compressive strain acting on the carcass folded-back portion 3 is reduced. This is because by bringing the carcass folded-back portion 3 closer to the carcass main body 2, the carcass folded-back portion 3 is brought closer to the neutral axis of bending, and the compressive action of the carcass folded-back portion 3 in that area is reduced. As a result, the compressive strain of the carcass folded-back portion 3 is suppressed, and fatigue fracture can be suppressed.

Furthermore, by gradually reducing the distance between the cords between the carcass main body 2 and the carcass folded-back portion 3, the distance between the carcass folded-back portion 3 and the outer surface increases, and the shear strain that occurs between the carcass folded-back portion 3 and the outer surface in this region is alleviated and reduced. As a result, separation between the carcass folded-back portion 3 and the rubber can be suppressed.

Also, by gradually increasing the distance between the cords between the carcass main body 2 and the carcass folded-back portion 3 from a minimum value toward the outside in the tire radial direction to a maximum value, the carcass folded-back portion in that region moves away from the neutral axis of bending, and the tensile force becomes even stronger, so the tensile strain increases. Therefore, as shown in Figure 3, the region T increases, and the action of the compressive force decreases by the amount of this increase. As a result, the compressive strain acting on the carcass folded-back portion 3 can be reduced, and fatigue fracture of the carcass can be suppressed.

As shown in FIG. 4, the center point of the cord of the carcass main body 2 at the minimum value is A, the center point of the cord of the carcass main body 2 at the maximum value is B, the center point of the cord where the normal line drawn from A to the carcass folded portion 3 intersects with the carcass folded portion 3 is A', and the center point of the cord where the normal line drawn from B to the carcass folded portion 3 intersects with the carcass folded portion 3 is B'. Let the distance between the cords A to A' be a and the distance between the cords B to B' be b.

At this time, the minimum cord distance a is preferably 0.18 to 0.40 times the maximum cross-sectional diameter of the bead core 1. In other words, if it is less than 0.18 times the maximum cross-sectional diameter of the bead core 1, the bending rigidity of the bead portion is insufficient, and the bead portion collapses significantly. This leads to an increase in the shear strain of the rubber present between the carcass folded portion 3 and the carcass main body portion 2. On the other hand, if it exceeds 0.40 times the maximum cross-sectional diameter of the bead core 1, the carcass folded portion 3 is too far away from the carcass main body portion 2, and the compression strain generated in the carcass folded portion 3 increases significantly. In addition, if the carcass folded portion 3 is too close to the outer surface of the bead portion, the shear strain of the rubber between the outer surface of the bead portion and the carcass folded portion 3 increases, making it impossible to improve the durability of the bead portion.

Now, as shown in Figures 1 and 4, if the height from the rim baseline L to point A of the carcass main body 2 where the minimum value is H _A , the height from the rim baseline L to point B of the carcass main body 2 where the maximum value is H _B , and the height from the rim baseline L to the rim flange 5 is H _f ,
1.26× _Hf ≦ _HA ≦2.14× _Hf , and
2.43×H _f ≦H _B ≦3.75×H _f
It meets the following criteria.

In other words, if H _A is less than 1.26 × H _f , the change in the minimum value of the distance between the bead core 1 and the cord becomes extremely large, and a sudden change in curvature is required to make the carcass folded-back portion 3 convex toward the carcass main body 2, making it difficult to manufacture the tire.
Furthermore, the bending rigidity of the bead portion near the lower end of the rim flange 5 decreases and the amount of collapse of the bead portion increases, resulting in a noticeable increase in shear strain acting on the rubber between the carcass folded-up portion 3 and the carcass main body 2.
In addition, this causes a significant increase in shear strain of the rubber along the carcass fold-back portion 3, leading to separation of the rubber on the carcass main body 2 side and the rim flange side of the carcass fold-back portion 3, thereby shortening the tire's lifespan.

On the other hand, if H _A exceeds 2.14 × H _f , the position of the minimum value will be too far outward in the tire radial direction relative to the area where compressive strain acts on the carcass folded-back portion 3, and the compressive strain will become large on the radially inner side (bead core side).
Furthermore, since the carcass fold-back portion 3 near the rim flange 5 has a shape that is convex in the opposite direction to the carcass main body portion 2, the shear strain acting on the rubber between the outer surface of the bead portion and the carcass fold-back portion 3 increases, making it difficult to suppress separation between the carcass fold-back portion 3 and the rubber.

In addition, by setting the height H _A in a region where the compressive strain generated in the carcass folded-back portion 3 begins to increase significantly, the advantageous effects of this embodiment can be further exhibited, so it is preferable to set the height H A to 1.4 × H _f ≦ H _A ≦ 1.9 × H _f .

Next, if H _B is less than 2.43 × H _f , the compressive strain acting on the carcass folded-back portion 3 at the position where the maximum value is reached becomes strong, and the effect of reducing the compressive strain by applying tensile strain to the carcass folded-back portion 3 decreases, making it difficult to suppress fatigue fracture of the carcass folded-back portion 3.

On the other hand, when H _B exceeds 3.75 × H _f , the maximum value is too far away from the region where the compressive force acts, so that the effect of applying tensile strain to the carcass folded-back portion 3 to reduce the compressive strain is reduced, and fatigue fracture of the carcass folded-back portion 3 cannot be suppressed.
Furthermore, in the sidewall region near the end of the carcass turn-up portion 3, the tension applied to the carcass turn-up portion 3 increases, and this tension acts in a direction in which the end of the carcass turn-up portion 3 is pulled out of the bead core 1. As a result, the shear strain of the rubber near the end of the carcass turn-up portion 3 increases, and cracks occur at the end of the carcass turn-up portion 3.

In addition, by setting the height H _B in a region where a strong tensile force is applied and the compressive force is reduced, thereby significantly reducing the compressive strain, the advantageous effects of this embodiment can be further exhibited, so it is preferable to set the height H B so that 2.8 × H _f ≦ H _B ≦ 3.4 × H _f .

Furthermore, the ratio b/a of the maximum inter-cord distance b to the minimum inter-cord distance a exceeds 1.00. In other words, if the ratio b/a is 1.00 or less, it becomes difficult to reduce the compressive strain. This is because, in a shape where the ratio b/a is 1.00 or less, the tensile force is not increased in the region T where tensile deformation occurs, and the effect of sufficiently reducing the compressive strain is lost. As a result, fatigue fracture of the carcass folded-back portion 3 cannot be suppressed.

Here, the thickness of the entire bead portion becomes thicker, particularly in the vicinity of the maximum value, and in order to avoid the occurrence of separation due to increased heat generation and heat accumulation in the rubber between the carcass folded portion 3 and the carcass main body portion 2, it is preferable to set the value to 1.40 or more and 4.00 or less.

Furthermore, in order to suppress fatigue fracture of the carcass folded portion 3 under heavy load or low internal pressure conditions, and to suppress increases in heat generation and heat accumulation in the rubber between the carcass folded portion 3 and the carcass main body portion 2, it is preferable to set the value to 2.00 or more and 3.00 or less.

The inventors conducted extensive research to solve the above problem and discovered that the carcass fold-back portion 3 had large curvature in certain areas, which caused the carcass fold-back portion 3 to buckle more severely, and this was the reason why fatigue fracture of the carcass fold-back portion 3 was not sufficiently reduced.

More specifically, when a point of large curvature occurs in a radial region of a certain length, the carcass cord of the carcass fold-back portion 3 deforms in two directions, the tire circumferential direction and the radial direction, due to buckling (in-plane bending deformation and circumferential bending deformation). When the carcass cord deforms in the above two directions, it deforms in a spiral shape, and if this deformation occurs repeatedly, the carcass cord will be destroyed by fatigue. This phenomenon is particularly noticeable when the carcass cord is a steel cord, as it cannot shrink in response to buckling. In addition, this phenomenon is particularly noticeable when the cord diameter of the carcass cord is small (specifically, when the diameter is 4.0 mm or less), as the rigidity against buckling is low.

In contrast, in the tire 8 of the present embodiment, the maximum value of the curvature of the carcass folded-up portion 3 in the tire radial direction region from a position spaced 2.0× _Hf to a position spaced 3.0× _Hf outward in the tire radial direction from the rim baseline is 0.003 (1/mm) or less. This makes it difficult for the carcass folded-up portion 3 to buckle, suppresses the above-mentioned spiral deformation, and suppresses the occurrence of fatigue breakage. In other words, if the maximum value of the curvature of the carcass folded-up portion 3 in the above-mentioned tire radial direction region exceeds 0.003 (1/mm), the carcass folded-up portion 3 buckles, the above-mentioned spiral deformation occurs, and fatigue breakage becomes more likely to occur.
As described above, according to the pneumatic tire 8 of the present embodiment, buckling of the carcass folded-up portion 3 is suppressed, thereby suppressing fatigue fracture of the carcass folded-up portion 3 and improving durability of the bead portion.

For the same reasons as above, in a tire radial region from a position spaced 2.0× _Hf to a position spaced 3.0× _Hf radially outward from the rim baseline, the maximum curvature of the carcass folded-up portion 3 is more preferably 0.0025 (1/mm) or less, and even more preferably 0.0020 (1/mm) or less. On the other hand, in order to smoothly form a carcass line in the tire radial region, the maximum curvature of the carcass folded-up portion 3 in the tire radial region is preferably 0.0001 (1/mm) or more.

In another embodiment of the tire of the present invention, in a tire radial region from a position spaced 2.0× _Hf to a position spaced 3.0× _Hf radially outward from the baseline of an applicable rim, the inter-cord distance between the carcass main body 2 and the carcass folded-up portion 3 is 0.25 times or more the maximum diameter of the bead core in the tire width direction cross section, and the maximum value of the curvature of the carcass folded-up portion 3 in the tire radial region is 0.003 (1/mm) or less.
If the inter-cord distance is less than 0.25 times the maximum diameter, the increase in shear strain acting on the rubber between the carcass folded-back portion 3 and the carcass main body 2 becomes significant, resulting in the occurrence of separation.
If the maximum value of the curvature of the carcass folded-up portion 3 in the above-mentioned tire radial direction region exceeds 0.003 (1/mm), buckling of the carcass folded-up portion 3 occurs, causing the above-mentioned spiral deformation, making it more likely to cause fatigue breakage.
As described above, the pneumatic tire 8 of the other embodiment can also suppress buckling of the carcass folded-up portion 3, thereby suppressing fatigue fracture of the carcass folded-up portion 3 and improving durability of the bead portion.
From the viewpoint of reducing the weight of the tire, it is preferable that the inter-cord distance be equal to or less than 0.40 times the maximum diameter.

In each of the above embodiments, the curvature of the carcass folded-up portion 3 at a position spaced 2.0× _Hf radially outward from the rim baseline is preferably smaller than the curvature at a position spaced 3.0× _Hf radially outward from the rim baseline. The area C in which the carcass folded-up portion 3 is subjected to a compressive force has a greater effect on fatigue fracture than the area T in which the carcass folded-up portion 3 is subjected to a tensile force, as shown in FIG. 1. Therefore, by making the curvature of the carcass folded-up portion 3 at a position spaced 2.0× _Hf radially outward from the rim baseline particularly small, the buckling of the carcass folded-up portion 3 is suppressed, thereby more effectively suppressing fatigue fracture of the carcass folded-up portion 3 and improving the durability of the bead portion.

In each of the above embodiments, in the tire radial direction region from a position spaced 2.0× _Hf to a position spaced 3.0× _Hf radially outward from the baseline of the applicable rim, it is preferable that the curvature of the carcass folded-up portion 3 gradually decreases from the outer side toward the inner side in the tire radial direction. As described above, the closer to the region C, the greater the influence on fatigue fracture. Therefore, by gradually decreasing the curvature as described above, the effect of suppressing fatigue fracture of the carcass folded-up portion 3 by suppressing buckling of the carcass folded-up portion 3 and improving the durability of the bead portion can be more effectively obtained. In addition, the carcass line can be formed smoothly.

In each of the above embodiments, it is preferable that the pneumatic tire is a heavy-duty tire, the end of the carcass fold-back portion 3 extends to the tire radial position of the sidewall portion, and the carcass cord is a steel cord. In the case of a heavy-duty tire, the problem of fatigue breakage of the carcass fold-back portion 3 tends to become more pronounced due to harsh usage conditions, and when the end of the carcass fold-back portion 3 extends to the tire radial position of the sidewall portion, it is easily subjected to the above-mentioned compressive and tensile forces, and when the carcass cord is a steel cord, as described above, it cannot be buckled and contracted, so the problem of fatigue breakage of the carcass fold-back portion 3 becomes more pronounced, and each of the above embodiments can be suitably applied in such cases. It is preferable that the end of the carcass fold-back portion 3 terminates, for example, radially outward of the maximum tire width position.

In each of the above-described embodiments, it is particularly preferable that the cord diameter of the carcass cord is 4.0 mm or less. This is because the stiffness of the carcass cord against buckling becomes low, and the problem of fatigue breakage of the carcass folded-back portion 3 becomes prominent, and in such a case, each of the above-described embodiments can be suitably applied.
Examples of the present invention will be described below, but the present invention is not limited to the following examples in any way.

Example 1
(Example 1)
The tire was a pneumatic radial tire for construction vehicles with a tire size of 59/80R63, mounted on a rim with a width of 1117.6 mm and a flange height _Hf of 127 mm, the internal pressure was adjusted to 600 kPa, and a lateral force of 149.5 kN was applied by moving the road surface laterally across the tire from a state in which a normal load of 996.4 kN was applied, and the buckling amplitude was measured at the point where the carcass folded-up portion of the carcass ply buckled the most. The tire structure was a carcass skeleton having a carcass main body portion made of a carcass ply with a rubber-coated multiple carcass cords that straddle a pair of bead cores in a toroidal shape, and a carcass folded-up portion made of the carcass ply that wraps around each bead core from the inside to the outside of the tire and extends radially outward from the carcass main body portion. The distance between the cords between the carcass main body and the carcass folded-back portion gradually decreases from the bead core toward the outside in the tire radial direction, reaches a minimum value once, and then gradually increases to a maximum value.
In addition, the compressive force acting on the carcass folded-up portion of the carcass ply is calculated by FEM calculation under simulation conditions that correspond to the same conditions as those under the actual measurement conditions described above.
(Comparative Example 1)
This example differs from Example 1 in that the carcass folded-back portion has a shape that does not have a maximum value of the inter-cord distance.
(Comparative Example 2)
The maximum value of the curvature of the carcass folded-up portion is different from that of the first embodiment.
The specifications and evaluation results of each tire are shown in the following Table 1. The compression strain and buckling amount are expressed as indexes with Comparative Example 1 being set at 100, and a smaller value indicates better performance.
The carcass ply buckling amounts were actually measured for Example 1, Comparative Example 1, and Comparative Example 2. The carcass ply compressive strains for Example 1, Comparative Example 1, and Comparative Example 2 were calculated by FEM calculation.

As shown in Table 1, the invention example had a reduced amount of buckling in the carcass ply compared to comparative examples 1 and 2. The invention example also had a reduced compressive strain in the carcass ply compared to comparative example 1.

5A and 5B are diagrams showing the radial curvature distribution and compressive strain distribution of the carcass folded-back portion in the tire, respectively. From Table 1, 5A, and 5B, it can be seen that in order to reduce the amount of buckling, it is necessary to reduce both the curvature and compressive strain of the carcass folded-back portion in the radial region of 2.0×H _f to 3.0×H _f .

[Contribution to the United Nations-led Sustainable Development Goals (SDGs)]
The SDGs have been proposed to realize a sustainable society. One embodiment of the present invention is considered to be a technology that can contribute to "No. 12 Responsible consumption and production" and "No. 13 Concrete measures against climate change."

1: bead core,
2: Carcass main body,
3: Carcass folded-up portion,
4: Applicable rim,
5: rim flange,
6: Belt,
7: tread portion,
8. Pneumatic tires

Claims (5)

A pneumatic tire having a carcass skeleton including a carcass body portion formed of a carcass ply in which a plurality of carcass cords are rubber-coated and toroidally straddle a pair of bead cores, and a carcass folded-up portion formed of the carcass ply that wraps around each bead core from the carcass body portion from the inside to the outside of the tire and extends radially outward in the tire,
In a cross-sectional view in the tire width direction when the pneumatic tire is mounted on the applicable rim,
the inter-cord distance between the carcass main body portion and the carcass folded-back portion gradually decreases from the bead core toward the outside in the tire radial direction, becomes a minimum value once, and then gradually increases to a maximum value,
heights H _A and H _B in the tire radial direction measured from the baseline of the applicable rim to the points of the carcass main body which are the minimum and maximum values, and a flange height H _f of the applicable rim,
1.26× _Hf ≦ _HA ≦2.14× _Hf , and
2.43×H _f ≦H _B ≦3.75×H _f ,
Fulfilling
a ratio b/a of the maximum inter-cord distance b to the minimum inter-cord distance a is greater than 1.00,
a maximum value of a curvature of the carcass folded-up portion in a tire radial direction region from a position spaced a distance of 2.0× _Hf to a position spaced a distance of 3.0× _Hf radially outward from the baseline is 0.003 (1/mm) or less. A pneumatic tire having a carcass skeleton including a carcass body portion formed of a carcass ply in which a plurality of carcass cords are rubber-coated and toroidally straddle a pair of bead cores, and a carcass folded-up portion formed of the carcass ply that wraps around each bead core from the carcass body portion from the inside to the outside of the tire and extends radially outward in the tire,
In a cross-sectional view in the tire width direction when the pneumatic tire is mounted on the applicable rim,
When the flange height of the applicable rim is _Hf ,
a cord-to-cord distance between the carcass main body portion and the carcass folded-up portion in a tire radial direction region from a position spaced apart by a distance of 2.0× _Hf to a position spaced apart by a distance of 3.0× _Hf outward in the tire radial direction from a baseline of the applicable rim is 0.25 times or more of a maximum diameter of the bead core in a cross section in the tire width direction,
A pneumatic tire, wherein a maximum value of a curvature of the carcass folded-up portion in the tire radial direction region is 0.003 (1/mm) or less. 3. The pneumatic tire according to claim 1, wherein the curvature at a position spaced a distance of 2.0× _Hf outward in the tire radial direction from the baseline is smaller than the curvature at a position spaced a distance of 3.0× _Hf outward in the tire radial direction from the baseline. The pneumatic tire according to any one of claims 1 to 3, wherein the curvature gradually decreases from the outer side toward the inner side in the tire radial direction in the tire radial direction region. The pneumatic tire is a heavy-duty tire,
An end of the carcass folded-up portion extends to a radial position of the sidewall portion,
The pneumatic tire according to any one of claims 1 to 4, wherein the carcass cord is a steel cord.

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